1. Field of the Invention
The present invention relates to a wire bonding method using a wire bonding apparatus.
2. Description of the Related Art
The wire bonding is a technique for connecting a semiconductor chip and a lead frame or the like with metal wires. To effect wire bonding, the semiconductor chip and lead frame are heated to a temperature suitable for wire bonding. It is known that an oxide film is made on the surfaces of a lead frame by the heating, causing poor bondage of the metal wires. The production of an oxide film presents a problem in die bonding, too. To solve the problem, it has been proposed to blow a hot gas to the lead frame prior to die bonding or jet a hot gas to the lead frame prior to wire bonding, thereby preventing the lead frame from being subjected to heat treatment for a long period of time. See JP 2000-235991 and JP 05-343446.
With an advancement of high-density mounting of multifunctional semiconductors, a lead frame type multichip package in which semiconductor chips are mounted on both the front and back surfaces of a lead frame has been proposed. However, the manufacture of the lead frame type multichip package has the following problem. The lead frame with one surface having been connected to a semiconductor chip with wires must be mounted on the heat plate such that the semiconductor and wires face downward. Consequently, it is necessary to provide a recess in the heat plate to receive the semiconductor chip and wires that have been mounted on the back side of the lead frame. The recess, however, reduces the heat transmission efficiency, preventing the semiconductor chip on the front surface of the lead frame from reaching the wire bonding temperature.